Previously, polyvinyl alcohol (hereinafter, also abbreviated as PVA) has been extensively used as a dispersant, an adhesive, a paste glue agent, a film, a paper processing agent, a coating agent or the like in various fields. For example, Encyclopedia of Pharmaceutical Excipients lists use of a partially hydrolyzed polyvinyl alcohol as a coating agent since it has water solubility and film forming property. However, when this is used by a spray method which is a conventional coating means, coating is very difficult due to remarkably spinnability (a finely-divided mist is not obtained but a spider web is obtained), and the partially hydrolyzed polyvinyl alcohol has scarcely been put into practice.
The present inventors have found that a polyvinyl alcohol polymer obtained by copolymerizing (hereinafter, also referred to as PVA copolymer), for example, emulsion-polymerizing polyvinyl alcohol, particularly, partially hydrolyzed polyvinyl alcohol with a polymerizable vinyl monomer, for example, acrylic acid and methyl methacrylate is easily dissolved in water, and it becomes possible to coat the solution with a conventional pneumatic spray nozzle without exhibiting spinnability. The present inventors have found that since a film of the thus obtained PVA copolymer is colorless, transparent, has no taste and no smell, and is excellent in physical properties such as strength, elongation rate and adhesive property, and has the property that gas permeability to oxygen is extremely low, the film is useful in protection of an easily oxidizable drug, masking of medicines, agricultural chemicals and foods having an offensive smell, suppression of whisker formation of a drug having sublimation property, use as an excellent binder for an oral solid preparation, or masking of drugs or foods exhibiting bitterness.
In addition, since such PVA copolymer has another characteristic that it is excellent in solubility in a solvent, and its solution has a remarkably low adhesive property, it is possible to coat fine particles such as fine granules and bulk therewith. By utilizing such excellent nature of the PVA copolymer, it has become possible to develop high concentration coating which can prevent interaction with other agent, modify a surface of a bulk, mask an offensive smell or bitterness and remarkably shorten a coating time has become possible.
Further, WO02/17848 discloses an invention of a hard capsule with excellent stability, containing a PVA copolymer as a main component, said hard capsule being prepared by filling a solution of a hardly soluble pharmaceutical component or a semi-solid into a capsule, but there has been no example of use of the PVA copolymer in coating medicines, drugs for animals, agricultural chemicals, fertilizers, foods and the like.
As described above, application range of the PVA copolymer as a coating agent is far wider as compared with other known coating agents which are currently used as a general-purpose polymer for film coating, and such PVA copolymer has excellent property. Accordingly, it can be expected that the PVA copolymer will serve as a substitute for such known coating agents in the future. In addition, as a result of various safety tests, any problem regarding safety has not been recognized until now in this PVA copolymer.